The adhesive layer of a medical adhesive tape to be adhered to the human skin for the protection of the skin, fixing something to the skin and the like, and a tape preparation for percutaneous absorption to administer a drug to the body through the human skin (preparation for percutaneous absorption) is required to have a sufficient adhesive force for adhesion to the skin, as well as the property to allow release or removal from the skin surface (cohesive force) after use, without staining (glue remainder and stickiness). The balance between the adhesive force and the cohesive force of such adhesive layer can be controlled by a suitable crosslinking treatment of an adhesive to be used, and various crosslinking treatments have been conventional by tried. As a crosslinking treatment of an adhesive, there are mentioned physical crosslinking by irradiation such as UV irradiation, electron beam irradiation and-the like, chemical crosslinking using a crosslinking agent such as polyfunctional isocyanate, organic peroxides, organometal compound, metal alkoxide, metal chelate compound, polyfunctional compound and the like, and the like.
Of the above-mentioned crosslinking treatments of the adhesive, however, the use of irradiation, organic peroxide or polyfunctional isocyanate sometimes results in a failure to cause-a crosslinking reaction or markedly low crosslinking efficiency, depending on the properties of the adhesive and the kind of additive. By these crosslinking treatments, moreover, a tape preparation for percutaneous absorption wherein an adhesive layer contains a drug may show decomposition of the drug to decrease the drug content.
It is known that, when a crosslinking agent, such as the aforementioned metal alkoxide and metal chelate compound, is used, such problems are not caused and a crosslinking treatment is affordable. However, the investigations by the present inventors have confirmed that an adhesive tape that has been crosslinked by the use of metal alkoxide or a metal chelate compound, particularly an adhesive tape containing a large amount of a plasticizer component, shows, after adhesion to the human skin surface for a long time, a cohesive force that was decreased with the lapse of time, which in turn results in a dramatic increase in the adhesive force during peeling off and staining of the skin surface (glue remainder, stickiness) due to the disintegration of the adhesive layer. While the occurrence of this phenomenon varies depending on the interindividual difference in the case of a relatively short period of application of within 24 hours, but observed at an extremely high frequency in the case of a long-term application of 48 hours or longer, irrespective of the interindividual difference.
The above-mentioned glue remainder and stickiness on the skin can be removed by wiping the skin with an alcohol solvent and the like. However, this wiping treatment is troublesome and some adhesive layers resist complete removal. Particularly in the case of a tape preparation for percutaneous absorption, an adhesive remainder on the skin may permit the drug in the residue to unexpectedly show efficacy even after removal of the preparation, which is potentially dangerous.
To deal with a cohesive failure during a long-term application to the human skin, it may be possible to increase the concentration of a crosslinking agent in the adhesive composition to increase crosslinking density, thus enhancing the initial cohesive force, and maintain a practical cohesive force even after a long-term application. However, an increased crosslinking density may cause a lower initial adhesive force (tackiness) to the skin, an increased amount of a crosslinking agent may shorten a pot life or produce a drug decomposition product and other problems.
As mentioned earlier, application for 24 hours or shorter does not generally cause a particularly serious problem, because the occurrence of glue remainder or stickiness varies depending on the interindividual difference. However, a function to stand a continuous application for a comparatively long period (not shorter than 2 days, sometimes about a week) has been increasingly requested in recent years for a medical adhesive tape or a tape preparation for percutaneous absorption to have. Thus, there is a demand for a medical adhesive tape or a tape preparation for percutaneous absorption having an adhesive layer that resists glue remainder and stickiness upon peeling off of the tape even after adhesion to the human skin for a long time of 48 hours or longer.